PHILADELPHIA  George W. Bush gained an advantage in numerous preconvention polls taken after he chose Dick Cheney as his running mate, but only three in 10 have a favorable view of the former secretary of defense.

And six in 10 in an ABC-Washington Post poll released over the weekend said they don't know enough about Mr. Cheney to form an opinion of him.

While a majority, six in 10, approve of Mr. Cheney, some of his positions caused negative reactions. Two-thirds felt less favorably about him after hearing that he is an oil company executive. About three-fourths were less favorable after being told of his votes against Head Start and the Older Americans Act that provides services to older people.

Three-fourths also said his selection will make no differ ence in their vote.

Among registered voters in the ABC-Washington Post poll, Mr. Bush had a 12-point lead over Mr. Gore, 49 percent to 37 percent in a four-way matchup with Green Party candidate Ralph Nader at 7 percent and Reform Party hopeful Pat Buchanan at 4 percent. Mr. Bush had a 5-point edge a week ago.

Mr. Bush had a 6-point lead in an NBC-Wall Street Journal poll released Sunday, with Mr. Nader at 8 points and Mr. Buchanan at 2 percent. Mr. Bush led Mr. Gore by 47 percent to 40 percent in a Newsweek poll, with Mr. Nader and Mr. Buchanan in low single digits.

Mr. Bush's lead is slightly higher in polls of likely voters, possibly a reflection of more intense voter support for the Texas governor and a history of higher voter turnout for Republicans.

A majority of voters in several polls said the selection of Mr. Cheney won't influence their votes, but the remainder were somewhat more positive about him. Conservatives at the Republican National Convention opening here today say they are enthusiastic about Mr. Cheney and his conservative record.

Conservatives were committed to Bush, said the Rev. Lou Sheldon of the Traditional Values Coalition, a group that lobbies for evangelical interests. The issue was 'Are you going to energize them and raise their level of awareness to create a greater-than-normal Republican turnout?'

Mr. Bush had a 20-point lead among independents and men, and split the women's vote in the ABC-Washington Post poll. He and Mr. Gore were about even in this poll a week ago.

The ABC-Washington Post poll of 1,208 taken Wednesday through Saturday had an error margin of 3 percentage points, slightly higher for registered voters. The Newsweek poll of 754 taken Wednesday and Thursday had an error margin of plus or minus 4 percentage points. The NBC-Wall Street Journal poll of 1,009 registered voters was taken Thursday and Friday and had an error margin of plus or minus 3 percentage points.